<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*border-radius:也是顺时针 */
        div{
            width: 100px;
            height: 100px;
            border: 20px solid red;
            border-radius: 50px;
        }
    </style>
</head>
<body>

<div>

</div>
</body>
</html>